The present disclosure relates to “active implantable medical devices” as defined by Directive 90/385/EEC of 20 Jun. 1990 of the Council of the European Communities, including implantable devices for continuous monitoring of the heart rhythm and delivery of electrical stimulation or resynchronization pulses to the heart if necessary. It relates more specifically to pacemaker leads to be implanted in the cardiac coronary network to allow stimulation of a left, ventricular or atrial cavity.
Unlike in right cavities, when it is desired to stimulate a left cavity, it is usually chosen to introduce a lead not into the cavity to be stimulated but in the coronary network. The lead is provided with an electrode applied against the wall of the epicardium and oriented towards the left ventricle or the left atrium, as appropriate.
Such a lead is for example the Situs LV model, marketed by Sorin CRM (Clamart, France) and described in EP0993840 A1 (Sorin CRM, previously known as ELA Medical). The introduction of such a lead is made by the coronary sinus opening in the right atrium, by endocardial access. The lead is then oriented and pushed along the coronary venous network to the selected pacing site. This intervention is very difficult given the particularities of the venous network and its access paths. These particularities may include the passage of valves, the tortuosity, and the gradual reduction in diameter of the conduit as the lead progresses into the selected coronary vein.
Once the target vein is reached, a satisfactory stimulation site must be found and it must be ensured that the chosen stimulation point does not generate phrenic stimulation.
In addition, a trend in recent developments in left ventricle pacing leads is the reduction of the diameter of the implantable part in the coronary network. The size of the lead body is indeed a factor directly related to the controlled guiding capacity of the lead in the venous coronary network, to be able to select specific stimulation sites located in certain collateral veins.
Thus, EP 2581107 A1 (Sorin CRM SAS) describes a lead including in its active distal part a microcable having a diameter of the order of 0.5 to 2 French (0.17 to 0.66 mm). This microcable includes an electrically conductive core cable formed by one or more strands of a plurality of composite strands, with a polymer insulation layer partially surrounding the core cable. The isolation layer is punctually exposed so as to expose the microcable in one or more points constituting a network of electrodes connected in series. The free end of the strand is also provided with a reported distal electrode.
EP 2455131 A1 (Sorin CRM SAS) discloses a lead of the same type, wherein the microcable slides in a lumen of a lead body, from which it can emerge over a length of 1 to 200 mm beyond the outlet of the lead body. The distal end of the lead body is provided with a sleeve of silicone assisting with its retention in a median region of the target vessel. From this position, the microcable is deployed into the vessel up to its distal active part (including the exposed portions forming the electrodes network) until it reaches the target region in a deep area of the coronary network.
In another embodiment described therein, the lead includes a plurality of microcables housed in as many separate respective lumens of a same lead body. The openings of the different lumens are axially shifted on the lead body, thus having a plurality of lateral openings from which the active parts of each of the microcables successively emerge.
One advantage of the very small diameter of the microcable is that it allows exploiting the entire length of the vein and cannulation of veins of very small diameter. Such areas have generally not been exploited until now due to the excessive size of conventional coronary leads. It, thus, becomes possible to treat areas difficult to reach, thereby making optimal use of all the veins present in the basal area. This may also lessen the risk of phrenic nerve stimulation which generally increases when the lead is too distal.
Moreover, the multiplication of stimulation points in a deep zone of the coronary network allows (unlike traditional leads) simultaneous stimulation of multiple zones of the epicardium in the region of stimulation, thereby improving the chances of optimal myocardium resynchronization.
With such a microlead, it is even possible to cross anastomosis (passages present from the end of certain veins to another vein), with the possibility of advancing the microlead in a first vein (“go” vein) followed by an anastomosis into a second vein (“return” vein) going back thereof. This may allow stimulation of the left ventricle from two distinct and remote regions. Finally, the structure of this microlead gives it great strength that guarantees its long-term biostability.
One of the difficulties with this type of microlead lies in the evaluation of the electrical stimulation site before the final placement of the microlead. Indeed, the implantation of a microlead of the aforementioned type is based on the use of a very thin catheter introduced to the target vein by conventional technique, with introduction of a guidewire into the venous system. The implantation proceeds by threading the catheter over this guidewire and finally by removal of the guidewire. The catheter in place helps guide the microlead to the stimulation site, and then this catheter is removed to expose the electrodes of the microlead and thus make them functional. This procedure does not allow anticipating the stimulation performance quality before the electrodes of the microlead are exposed in the final position thereof. Furthermore, this type of lead including a microcable does not have a very good tracking performance, that is to say the ability to progress into the venous system by push and torsion manipulation of its proximal end.
A microcable is indeed much more deformable than a guidewire, which is specially designed to navigate into the venous system. A guidewire typically has the required properties of “torquability” (ability to transmit over its entire length to the distal end a rotation given by an operating handle from the proximal end) and “pushability” (ability to progress in the biological network without jamming, under the effect of a push exerted from the proximal end with the operating handle). These properties are important for navigation in the coronary network.
It is therefore very difficult to introduce and guide a microcable directly into the venous system. For these reasons, it is also very difficult to change the position once it has been set up, such as in searching for better stimulation sites. Further, it is extremely difficult to make it go back to then select another vein or pass through an anastomosis.
It is thus desirable to evaluate as early as possible during the implantation procedure the best placement position of the microlead and its electrodes, to be able, if necessary, to modify this position or even to consider repositioning the microlead in another vein of the coronary network.